Electronic control system for remote control circuit breakers

ABSTRACT

An improved electronic control system for a remote control circuit breakers is disclosed. The system employs digital type logic modules which respond to closure and opening of a remote pilot control breaker to initiate and time the duration of energization of set and trip coils of the circuit breaker electromagnetic operator. The modules are so interconnected with RC and transistor circuits that they will automatically respond to, and function equally well, when auxiliary DC power only is available.

United States Patent 1191 Ryczek et al.

ELECTRONIC CONTROL SYSTEM FOR REMOTE CONTROL CIRCUIT BREAKERS Inventors: Lawrence J. Ryczek, East Troy; Walter L. Rutchik, Wauwatosa; Donald L. Van Zeeland, Franklin, all

of Wis.

Assignee: Cutler-Hammer, Inc., Milwaukee,

Wis.

Filed: Sept. 13, 1973 Appl. No.: 396,733

US. Cl. 317/33 SC, 307/14l.8, 317/36 TD, 317/54 Int. Cl. H02h 3/08 Field of Search 3l7/33 SC, 60, 13 R, 54, 317/36 TD; 307/l4l.8, 115, 208

References Cited UNITED STATES PATENTS Soos r. 3l7/l3R Nov. 5, 1974 3,706,916 12/1972 Halbeck et a] 317/33 SC Primary Examiner-James D. Trammell Attorney, Agent, or F irm H. Rather; Wm. A. Autio An improved electronic control system for a remote control circuit breakers is disclosed. The system employs digital type logic modules which respond to closure and opening of a remote pilot control breaker to initiate and time the duration of energization of set and trip coils of the circuit breaker electromagnetic operator. The modules are so interconnected with RC and transistor circuits that they will automatically respond to, and function equally well, when auxiliary DC power only is available.

ABSTRACT 6 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION U.S. Pat. No. 3,706,916 discloses and claims a re- I mote control circuit breaker system which is particularly suitable for use in large jet aircraft. As disclosed that circuit breaker system uses electronic control together with mechanically operated cut-throat contacts for controlling the energization of set and trip" coils of the circuit breakers electromagnetic operator in response to the closing and opening of a remotely located pilot control circuit breaker. The electronic control additionally responds to trip-open of the main circuit breaker to subject the pilot breaker to a controlled value of simulated over-load current that will cause the latter to trip open and afford indication of opening of the main circuit breaker.

The operation of the aforementioned cut-throat contacts is dependent upon the armature of the electromagnetic operator attaining one or the other of its extreme positions. The required adjustment of such contacts to open in correspondence with the armature attaining its sealed positions is critical. If they open too soon the armature may not attain sealed position, or if they fail to open coil burn-out can result. A nonmechanical way of effecting deenergization of these operating coils of the electromagnetic operator is highly desirable.

OBJECTS OF THE INVENTION It is a primary object of the present invention to provide an improved electronic control system for remote control circuit breakers of the aforementioned type which will after effecting energization of either the set or trip coils of the electromagnetic operator of the circuit breaker deenergize the same without need for cutthroat contacts.

A further object of the invention is to provide an electronic control system of the aforementioned type which is characterized by affording timed pulses of current to the set and trip coils for a duration sufficient to insure that the armature of electromagnetic operator will transfer from one to the other of its extreme sealed positions.

Another object of the invention is to provide an electronic control system of the aforementioned type which can function equally well when supplied with either or both main AC power and auxiliary DC power.

A more specific object is to provide an electronic control system of the aforementioned type wherein digital type logic modules are utilized to initiate triggering the energization of the set and trip coils in response to the closing and opening of the remote pilot control breaker, and

A still further specific object of the invention is providing an electronic control system of the aforementioned type wherein said digital type logic modules also initiate deenergization of said set and trip coils a predetermined timed interval following energization of the latter.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a diagramatic showing of a remote control circuit breaker system which incorporates the improved electronic control of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows an improved remote control circuit breaker system as applied to a typical three phase, 1 15/200 volt, 400 Hz alternating current power supply, and an auxiliary 28 volt DC. power supply, such as found on large jet aircraft. It comprises independent bimetal thermal elements l0 l0" and 10 connected in series in each of the three phase supply lines A, B and C, respectively, and main load contacts l2", l2 and 12 that are connected in series with thermal elements 10", 10" and 10, respectively and to a load 13.

The contacts 12, 12 and 12 are electromechanically closed by energization of a set coil S, and opened by energization of a trip coil T as will hereinafter be explained. Energization and deenergization of coils S and T is initially by operation of a remote pilot circuit breaker RPB which would be located in the flight deck for operation and monitoring by flight personnel. Overload trip contacts OLT, which are normally held open upon normal opening and closing of contacts l2", l2", and 12 as directed by the pilot control circuit breaker, are caused to trip closed upon occurance of an overload for a purpose that will hereinafter be explained. The construction and purpose of coils S and T and contacts OLT is basically the same as that described in the Halbeck et al. U.S. Pat. No. 3,706,100 and in the copending Mallonen application Ser. No. 409,785 filed Oct. 26, I973 and assigned to the assignee ofthis application.

The novelty in the present invention resides in the improved electrical and electronic circuitry now to be described for controlling the energization and deenergization of coils S and T, and causing the trip open of pilot circuit breaker RPB upon occurance of overload response and opening of main breaker contacts l2, l2 and 12". These circuits are supplied with rectified AC from lines B and C through diodes D1 and D2 which are connected to a junction point 14. Trip coil T is connected at one end in series with a line 16 and a resistor R1 to junction 14 and at its other end in series with the main conducting path of a semi-conductor controlled rectifier SRCI to ground. Set coil S is also connected at one end to junction 14 in series with line 16 and resistor R1 and at its other end in series with the main conducting path of SCR2, like SCRl, to ground. The control electrodes of SCRl and SCR2 are connected through filter capacitors Cl and C2 to ground respectively, control electrode of SCRI is connected to the output terminal 10 of NOR logic unit ICZD of an integrated circuit module IC2, and the control electrode of SCR2 is similarly connected to the output terminal ll of NOR unit IC2B of module IC2.

As will be appreciated control electrode of SCRI will be subjected to a firing current wherever the output of unit IC2A is at logic I level and similarly the control electrode of SCR2 will be subjected to a firing current whenever the output terminal of logic unit IC2B is at a logic I level.

A diode D3 which has its anode connected to line 16 is connected in series with overload trip contacts OLT and a thermistor TH through a line 18 to a terminal 3. Terminal 3 has connection through a line 20 to one side of remote pilot circuit breaker RPB which at its other side is connected to ground. The point common between contacts OLT and thermistor TH is connected in series with a resistor R2 to the base of a transistor Q2. The collector of a transistor Q2 and terminal 3 is connected in series with a resistor R3 to the collector of a transistor Q3 and to the interconnected bases of transistors Q2 and Q3. The collector of transistor O1 is connected to the upper plate of a capacitor C3 which has its other plate connected to ground. The emitter of O1 is connected to the base of an N-P-N transistor Q4, and in series with the collector-emitter circuit of O4 to ground. The emitter of transistors Q2 and Q3 are connected to ground.

A pair of capacitors C4 and C5 are connected in series between line 16 and ground, and serve as high frequency noise filters to prevent unwanted turn-on of either SCR] or SCR2. Diodes D4 and D5 connected in series between ground and line 16 prevent the anodes of SCRl and SCR2 from swinging negative. Diodes D6 and D7 are connected across coils'T and S respectively in the reverse conducting relation shown to prevent the coils from being subjected to inductive transients when either of them are switched off, and to provide coil circulating currents when switched on.

Junction point 14 of the power supply is connected in series with a diode D8, a resistor R4, a diode D9 and voltage divider resistors R5 and R6 to ground. A capacitor C6 is connected from the junction point 20 between diode D9 and resistor R5 to ground. A diode D10 has its anode connected to the point common between coil T, the anode of SCRl and the anode of diode D6 and its cathode to junction point 20. Similarly, a diode D11 has its anode connected to the point common between coil S, the anode of SCR2 and the anode of diode D7, and its cathode to junction point 20. Diodes D10 and D11 couple the anodes of SCR1 and SC R2 to capacitor C6 for dv/dt protection.

Auxiliary D.C. power at 28 volts may be assumed to be applied at terminal 22. Terminal 22 is connected in series with an inductor L1 to a junction point 24, and a diode D12 is connected from ground to junction point 24. lnductor Ll prevents high frequency high current oscillation, and diode D12 suppresses negative transient spikes. Junction point 24 is connected in series with a diode D13 to the point common between diode D3 and contacts 0LT, and is connected in series with diodes D14 and D15 to the point common between D8 and resistor R4. It will be seen that in the absence or cut-off of A.C. supply power the OLT contact circuit and voltage divider resistors R5 and R1 will be supplied with D.C. control power from D.C. input terminal 22. Diodes D13, D14 and D15, and diode D8 serve to decouple the A.C. and D.C. power supply sources from each other.

An N-P-N transistor Q5 has its cathode connected in series with a diode D16 to line 16. Another N-P-N transistor Q6 has its collector-emitter circuit connected between the collector and base of O5 in a darlington configuration and has its base connected to the collector of a P-N-P transistor Q7. Bias resistors R7 and R8 are connected across the emitter-base circuits of Q5 and Q6 respectively.

A resistor R9 is connected across the emitter and base of Q7 and the point common between the base of Q7 and resistor R9 is connected in series with a resistor R11 to the collector of an N-P-N transistor Q8 which has its collector connected to ground. A zener diode ZDl is connected between the collector and emitter of 08 as shown to provide transient voltage protection thereacross. The base of O8 is connected in series with a resistor R10 to the output terminal of logic unit lCl with a capacitor C7 connected between the base and collector of Q8. The junction point 20 is connected in series with resistors R11 and R12 to one input terminal of logic unit lC2C of [C2, respectively, and such junction point is also connected in series with a resistor R13, a line 26, a capacitor 8 to an input terminal of logic unit lC ID of lCl, and to an input terminal of logic unit lC2B of 1C2.

A zener diode ZD2 has its anode connected to ground and its cathode connected to the point common between resistor R13 and line 26 and acts as a voltage regulator. The point common between diodes D14 and D15 is connected in series with a resistor R14 to line 26. The point common between dioded D8 and D15 is connected through line 28 and a resistor R15 to input terminal of logic units IC2D and IClC. Line 28 is also connected through a resistor R16 to input terminals of logic unit IC2B and IClD, respectively.

Both input terminals of logic unit IC2A and both input terminals of logic unit ICZB are connected through a line 30 to the point common between the collector of transistor Q1 and capacitor C3. The logic output of IC2C is connected in series with a capacitor C9 to the point common to resistor R15, and the aforementioned input terminals of logic unit [C2D and IClC. The logic output terminal of IC2D is connected in series with a reversely poled diode D17 to the aforementioned input terminal of logic units IC2B and IC 1D and to the upper plate of a capacitor 10 which has connectors through its lower plate to ground. A resistor R18 is connected at one end to the point common between resistor R12 and terminal 3, and at its other end to a point common between capacitor C8 and another input terminal of logic units lC2B and lClD.

The point common between voltage divider resistors R5 and R6 is connected to an input of logic unit IClA. The logic output terminal of logic unit lClB is connected to the other input terminal of IC 1A. Logic unit IClB has one of its input terminals connected to the output terminal of logic unit lClC and its other input terminal connected to the output terminal of logic unit lClD.

DESCRIPTION OF OPERATION OF THE REMOTE CONTROL CIRCUIT BREAKER SYSTEM With lines A, B and C energized to provide 1 15/200 volts D.C., it will be observed that rectified A.C. will be supplied through dioded D1 and D2, and that such rectified circuit will flow through resistor R1 into line 16, and through diode D8 into line 28, and through resistor R4 and diode D9 to charge capacitor C6. Resistors R5 and R6 will be subjected to the potential of C6, and thus supply a logic 1 level to the upper input terminal of logic unit IC1A. This results in a logic 0 at the output of the latter. Consequently, transistor Q8 will be biased into non-conduction, and as a result transistors Q5, Q6 and Q7 are correspondingly held off when the voltage of the A.C. supply is normal.

Now let it be assumed that trip coil T has been previously energized and that contacts 12, 12" and 12 are open and that pilot circuit breaker RPB is open with RPB open terminal 3 and line 18 will rise to a high potential. The lower input terminal to logic unit IC2B will through resistor R18 then be subjected to a logic 1 level thereby causing a logic 0 at the output terminal of the latter. Thus the control gate of SCR2 will be at a low potential preventing conduction of SCR2. Also through resistor R12 both input terminals to unit IC2A will be at a logic 1" level and thus the output terminal of the latter will be at logic 0. Consequently, capacitor C will not charge.

Now assume that RPB is closed. Terminal 3 then goes to ground logic 0" level, and the input terminal to IC2A then goes to logic 0 level and the output of the latter goes to logic I," but capacitor 10 does not immediately charge as diode D17 blocks. The other input terminals to lC2B follow terminal 3T 0 level, and thus its output terminal goes to logic 1 which results in the control electrode of SCR2 being subjected to the potential which turns the latter on. When SCR2 turns on current flows through diodes D1 and D2, resistor R1, line 16, coil S and SCR2. This results in coil S being energized to operate the electromechanical operating mechanism and cause closure of circuit breaker main contacts 12, 12" and 12 Capacitor 10 is charged by current flowing through line 28 and resistor R16. When the charge potential on C10 reaches a high enough value for the upper input terminal of lC2B to see a logic 1 level, the output of the latter shifts to a logic 0 thereby removing the firing potential from the control electrode of SCR2. With rectified AC flowing through SCR2 the latter will then turn off on the next current zero point. The value of capacitor C10 and R11 are selected to provide an RC time constant that will insure SCR2 and coil S being maintained energized sufficiently long to effect closure of the main circuit breaker contacts l2", l2" and 12".

With the main circuit breaker contact closed, and RPB closed the two input terminals of lC2C will be at ground or logic 0" which results in the output terminal of the latter being a logic 1 level. Thus capacitor 9 will have no charge on it, and the two input terminals to lC2D will be at logic 1" levels which results in the output terminal of the latter being at a logic 0 level. Thus the control electrode of SCRl will be at a potential preventing conduction of the latter.

Now let it be assumed that RPB is opened. The input terminals to lC2C follow the rise in potential at terminal 3, and immediately go to a logic 1 level, and the output terminal of the latter correspondingly goes to a logic 0" level, as do the input terminals of IC2D.'Thus the output terminal of lC2D goes to a logic 1 level causing the control gate of SCRl to be subjected to a firing current and SCRl then turns on. Rectified AC current then flows through diodes D1 and D2, resistor R1, coil T and SCRl. Coil T is thus energized to cause the electromechanical operating mechanism to open main breaker contacts 12", 12" and 12.

Capacitor 9 which was previously discharged begins to charge when the output terminal of lC2C terminal goes to a logic 0" level. When the charge potential of capacitor 9 reaches a logic 1" level, the upper input terminal of lC2D being subjected to such potential causes the output terminal of the latter to shift to a logic 0 level. Consequently SCRl will thereafter turn-off on the next zero point in the rectified AC current. The value of capacitor C9 and resistor R15 are selected to provide an RC time constant that will insure SCRl and coil T being maintained energized suffciently long to complete opening of contacts 12, 12, and 12.

Assume that main breaker contacts 12", 12" and 12" are closed and RPB are closed. Now let it be assumed that one or more of the bimetal elements 10'', 10 and 10 is subjected to a high overload current flowing therethrough. As more fully described in the aforementioned U.S. Pat. No. 3,706,916, this causes a latch to trip which in turn causes main breaker contacts 12, 12" and 12 to open. Simultaneously, overload trip contacts 0LT close.

With contacts OLT closed a high rectified A.C. current flows through one or both of diodes D1, D2, resistor R1, line 16 diode D3, contacts 0LT, then in one branch through thermistor TH line 18 and the RPB to ground. Current also flows from resistor R2 through the base emitter circuit of transistor Q1, the collectoremitter and base emitter circuits of O4 to ground. Current also flows from resistor R2 through the collectoremitter circuit of O2 to ground, and from thermistor TH through resistor R3, and the base emitter and collector emitter circuits of O3 to ground.

The voltage drop across thermistor TH causes the voltage drop across resistor R2 to be greater than across resistor R3. Thus initially more current is available at the collector of Q2 than at the collector of Q3. Consequently, transistor Q1 and OS are turned on clamping line 30 to ground. With line 30 clamped to ground the input terminals to logic units lC2A and IC2C will remain at logic 0 levels, which as will be seen, results in the control electrodes of SCRl and SCR2 being held also at logic 0 level which prevents them from being turned on.

After a short period of the aforementioned heavy current flowing through thermistor TH and RPB, on the order of milliseconds, the thermal element in RPB will normally respond to cause opening of the latter. Thereafter the current flow through resistor R3 becomes greater than the current flow through resistor R2. Consequently, the collector emitter circuit of Q3 takes more of the current and there will no longer be excess current sufficient to hold Q1 on and the latter turns off thereby allowing line 30 to rise to a logic 1 level. Thus the output of lC2C goes to logic 0 and the output of lC2D to logic l whereupon the control electrode of SCRl is energized to cause the latter to turn on and energize trip coil T as hereinbefore described. Accordingly the electromagnetic armature of the main circuit breaker is caused to operate to the point wherein main contacts 12, 12 and 12 are held open pending reclosing of remote pilot breaker RPB. As described in U.S. Pat. No. 3,706,916, the transfer of the armature of the electromagnetic operate effects reopening of overload trip contacts OLT.

As aforedescribed in U.S. Pat. No. 3,706,916 thermistor TH also functions to limit current flow through line 18 and pilot control breaker RPB if a fault should occur. If a fault should occur in line 18 or breaker RPB, the high current flowing through TH will cause its temperature to rise and when C is reached a very marked increase in ohmic resistance of TH occurs thereby limiting the current flow therethrough.

In the operation of the remote control circuit breaker and remote pilot control breaker hereinbefore described, it is assumed that lines A, B and C were adequately energized with 1 15/200 volt, 400 Hz AC supply, and that 28 volt DC was available at terminal 22. lt will be observed that in that circumstance diodes D3 and D13 decouple the DC. voltage from the LT. In the event of faults in any of the AC. buses A to B and contacts OLT close, current flows therethrough is derived by DC. current flow through diode D13.

Let it be assumed that there has been a failure in the AC power supply. In that instance the 28 volt DC power supply will take over to provide operation of the RCCB. If RPB is either open or closed, the output terminals of lC2B and IC2D will be at logic 0" output and thus SCRl and SCR2 will be prevented from conduction.

Now with 28 volts DC flowing through resistor R4, diode D9, capacitor C6 and voltage divider resistors R5 and R6, the voltage at the point common between the latter two resistors and the upper input terminal of lClA will be sufficiently low that the latter terminal will be at a logic 0 potential. The ratio of ohmic resistance is selected that the resistance of R5 is times that of R6. This will insure that with rectified AC voltage of 100 across R5 and R6, that the upper input terminal of lC 1A will be at 5 or greater volts to provide a logic 1 potential, and when 28 DC volts is present across R5 and R6 it will be at a voltage providing logic 0." With both input terminals of lClA at logic 0" the output terminal of the latter will then be at a logic 1 potential which will then render transistor Q8 conducting. With Q8 conducting the potential on base of transistor Q7 will be reduced to a point where it is rendered conducting. Transistors Q6 and Q5 will correspondingly rendered conducting and DC power can then flow through line 26 and diode D16 into line 16. Thus whenever SCRl or SCR2 are triggered into conduction as aforedescribed DC energizaing current will be available to energize latter coil T or coil S as the case might be.

It will be observed from the foregoing that the input terminals of ICZD and IC 1C are connected in parallel with the output terminal of IC2C. Consequently the output of lClC will always be at the same logic level as the output of IC2D. Similarly, the input terminals of lClD are connected in parallel with the input terminals of [C28, and consequently the output lClD will always have the same logic level as the output of lCZB. With pilot control circuit breaker RPB open, the outputs of lClC and [C1D will then be at logic 0 levels. Thus the output of lClB will be at a logic 1" level, and with the upper input terminal of lClA at logic 0" level, and its lower input terminal at logic 1 level the output of lClA will be at a logic 0" level. Thus transistors Q8, Q7, Q6 and Q5 will all be non-conducting, and no D.C.

' current will flow in lines 26 and 16.

Now let it be assumed'that pilot circuit breaker RPB is closed. As aforedescribed, this results in the output of [C2B going from a logic 0" to logic I level while the output of lC2D is held at a logic 0 level. Thus the output of [C 1C will be at logic 0" and the output of lClD will be at logic 1. Accordingly the output of lClB will shift from logic 1 to 0 level, and with both inputs of lClA at logic 0 levels the output of the latter will shift to logic 1 level resulting in conduction of transistor 08, Q7, Q6 and Q5 and consequently supply of DC. current to lines 26 and 16. SCR2 and set coil S will thus be energized from the aforementioned timed interval to cause closing of contacts 12, 12 and 12 When pilot circuit breaker RPB is thereafter opened, the output of [C2D shifts to a logic 1 level while that of [C28 remains at 0 level. Accordingly the output of lClC shifts to a logic 1 level while the output of lClD remains at logic 0. Thus IClB will have its input terminals at logic 1 and 0 levels thus providing logic 0" at its output. lClA will then have logic 0 levels at both input terminals to cause a shift to logic 1 at its output terminal and effect consequent turn-on of transistor Q8, Q7, Q6 and OS for a timed interval and provide current flow through lines 26 and 16 to energize SCRl and trip coil T.

As aforedescribed SCRl and SCR2 of course are only energized for timed intervals, and are rendered non-conducting when the outputs of [C2D and lC2B revert back to logic 0 levels. It will be seen then that when this occurs both inputs to [C18 will then be at logic 0 thus effecting a shift to logic 1 at the output of the latter. Consequently the output of lClA shifts back to logic 0 thus rendering transistors Q8, Q7, Q6 and Q5 non-conducting thereby removing DC current from lines 26 and 16.

It will be understood from the foregoing, that upon closing of overload trip contacts 0LT pilot breaker RPB is ultimately caused to open. Thus 1C1 will function as above described for normal manual opening of RPB to provide for turn-on of transistors Q8, Q7, Q6 and O5 to afford supply of DC. current to lines 26 and 16.

We claim:

1. In an electronic control for a remote control circuit breaker system in which a main circuit breaker is normally operated by energization of electromagnetic set and trip coils in response to the opening of a pilot control circuit breaker and in which overload trip-open of the main circuit breaker results in closure of overload trip contacts to initiate flow of a controlled current through the pilot control circuit breaker to cause the latter to open, the improvement comprising means responsive to the manual closing and opening of said pilot control circuit breaker to initiate corresponding energization of one or the other of said set and trip coils and thereafter deenergize the same after electrically timed intervals.

2. The combination according to claim 1 wherein said means comprises means for controlling the supply of DC. energizing current to the set and trip coils in event of loss of main AC power, said last mentioned means being responsive to presence of normal AC power to block flow of DC energizing current, and being responsive to absence of normal AC voltage to make auxiliary DC power available to energize said set and trip coils.

3. The combination according to claim 1 wherein said means comprises first and second digital logic switching means, and first switching means responding to closure of said pilot control circuit breaker to initiate energization of said set coil, and said second switching means responding to opening of said pilot control circuit breaker to initiate energization of said trip coil.

4. The combination according to claim 3 wherein each of said switching means includes timing circuit means which cause each of the latter to switch to coil deenergizing states after a timed interval following its switching to the coil energizing state.

10 gize said set and trip coils under the direction of said first and second switching means.

6. The combination according to claim 5 wherein said third digital logic switching means includes means responsive to action of said timing circuit means to provide coil deenergizing states to render said transistor means non-conducting to remove auxiliary DC power from said set and trip coils. 

1. In an electronic control for a remote control circuit breaker system in which a main circuit breaker is normally operated by energization of electromagnetic set and trip coils in response to the opening of a pilot control circuit breaker and in which overload trip-open of the main circuit breaker results in closure of overload trip contacts to initiate flow of a controlled current through the pilot control circuit breaker to cause the latter to open, the improvement comprising means responsive to the manual closing and opening of said pilot control circuit breaker to initiate corresponding energization of one or the other of said set and trip coils and thereafter deenergize the same after electrically timed intervals.
 2. The combination according to claim 1 wherein said means comprises means for controlling the supply of D.C. energizing current to the set and trip coils in event of loss of main A.C. power, said last mentioned means being responsive to presence of normal AC power to block flow of DC energizing current, and being responsive to absence of normal AC voltage to make auxiliary DC power available to energize said set and trip coils.
 3. The combination according to claim 1 wherein said means comprises first and second digital logic switching means, and first switching means responding to closure of said pilot control circuit breaker to initiate energization of said set coil, and said second switching means responding to opening of said pilot control circuit breaker to initiate energization of said trip coil.
 4. The combination according to claim 3 wherein each of said switching means includes timing circuit means which cause each of the latter to switch to coil deenergizing states after a timed interval following its switching to the coil energizing state.
 5. The combination according to claim 4 wherein said means further comprises third digital logic switching means and transistor means for controlling the supply of D.C. energizing current to the set and trip coils in the event of loss of main AC power, said third switching means being responsive to the presence of normal AC power to block conduction of said transistor means, and also being responsive to the absence of normal AC voltage to render said transistor means conductive to make auxiliary DC power available to energize said set and trip coils under the direction of said first and second switching means.
 6. The combination according to claim 5 wherein said third digital logic switching means includes means responsive to action of said timing circuit means to provide coil deenergizing states to render said transistor means non-conducting to remove auxiliary DC power from said set and trip coils. 